1. Field of the Invention
The present invention relates to a radio transmission system (also including a radio communication apparatus which is realized in a single housing), a transmission-side radio communication apparatus, and a radio transmission method. In particular, the present invention relates to a mechanism for transmitting a plurality of transmission-target signals by radio using space division multiplex.
2. Description of the Related Art
For example, as a method which realizes high-speed signal transmission between electronic instruments arranged at a comparatively short distance (for example, within several centimeters to ten-odd centimeters) or within an electronic instrument, an LVDS (Low Voltage Differential Signaling) is known. However, recent increases in the capacity and speed of transmission data have led to problems, such as an increase of power consumption, an increase of the effect of signal distortion due to reflection or the like, an increase of unnecessary radiation, and the like. For example, when a signal, such as a video signal (including a captured signal) or a computer image, is transmitted at a high speed (in real time) within the instrument, the LVDS has limitations.
In order to cope with a problem regarding the high speed of transmission data, it is possible to increase the number of wirings or to reduce the transmission speed per signal line through signal parallelization. However, such a countermeasure results in an increase in the number of input/output terminals. As a result, a printed substrate or a cable wiring is complicated, or a semiconductor chip increases in size. Further, high-speed and large-capacity data is routed through wirings, thus so-called electromagnetic interference becomes problematic.
The problems in the LVDS or the method in which the number of wirings increases are due to signal transmission through electrical wirings. Thus, as a method which resolves the problems due to signal transmission through electrical wirings, it is possible to transmit signals by radio without using electrical wirings.
When a plurality of communication sections are provided on the transmission side and the reception side to perform multiplex transmission, it is also possible to apply space division multiplex. However, when space division multiplex is applied, it is necessary to provide a countermeasure against interference between channels. As one method which resolves this problem, it is possible to apply MIMO (Multi-Input Multi-Output) (for example, JP-A-2009-055228, JP-A-2009-049632, and JP-A-2009-033588).
JP-A-2009-055228, JP-A-2009-049632, and JP-A-2009-033588 are intended for radio transmission at a comparatively long distance with respect to radio transmission within an instrument or between instruments, and describe the application of MIMO processing in combination with an OFDM modulation scheme. That is, the MIMO processing described in JP-A-2009-055228, JP-A-2009-049632, and JP-A-2009-033588 depends on the OFDM modulation scheme.